The present invention relates generally to an antenna system. More particularly, the present invention is directed to a multi-channel, circularly polarized antenna that is suitable for high power broadband multiplexing.
Under the rules of the Federal Communication Commission (FCC), television (TV) broadcasters are required to complete a transition from their current National Television System Committee antenna systems to digital television (DTV) antenna systems by the year 2006. To fulfill the requirements of the FCC, TV broadcasters are installing DTV antenna systems on their existing antenna towers.
Historically, radio frequency (RF) station operators including, for example, frequency modulation (FM) radio station operators, lease tower space from TV stations to accommodate their FM antennas. However, TV station operators, in their attempts to go on-air with DTV, are finding that the addition of DTV antennas to their antenna towers limits the amount of tower space available to accommodate the antennas of the FM radio station operators.
The addition of the DTV antennas to the existing antenna towers has not only reduced the amount of space available for leasing out, but has also driven up both the weight loads and windloads of those existing antenna towers. The number of antennas that can be installed on an antenna tower is limited to the amount of tower space, the amount of weight the tower can withstand and/or the amount of windload the tower can withstand. Accordingly, a tower can only withstand a certain amount of weight and/or windload before the tower fails in its support functions.
Constucting new towers is sometimes not a feasible solution. Aside from the high cost of tower construction, difficulties arise in finding an acceptable location and in obtaining construction permits. Community members near the proposed construction site may oppose the building of antenna towers in their communities. In addition, tower construction may be limited to locations where the environmental conditions are suitable for the erection of an antenna tower. For example, it may sometimes not be suitable to bulid antenna towers where the moisture level in the soil is high.
To alleviate overcrowding and potentially overloading antenna towers, radio station operators have turned to sharing multi-channel antennas. Multi-channel antennas are capable of transmitting more than one station, and thus, it is possible to avoid having an antenna for every FM station.
However, there are disadvantages of utilizing conventional multi-channel FM antennas, such as circularly-polarized FM muliplex dipole antennas and circularly-polarized broadband panel antenna arrays. For example, a conventional circularly-polarized FM multiplex dipole antenna is typically a sidemount antenna. When signals are transmitted from sidemount antennas, the signals tend to reflect off of the legs of the antenna tower and inhibit the FM antenna from generating a circularly-polarized/omnidiretional azimuth pattern. Consequently, the signal coverage is reduced. In addition, the amount of reflection is typically attributed to the frequency of the signals being transmitted. Often, the greater the frequency, the greater the amount of reflection, and the greater the effects on the azimuth pattern.
FM multiplex antennas should be designed to transmit signals of varying frequencies. Thus, there is difficulty in designing the conventional circularly-polarzied FM multiplex dipole antenna to generate a consistent azimuth pattern across the full FM band because the azimuth pattern varies with frequency. Accordingly, it is difficult to provide consistent signal coverage across the full FM band. In addition, the conventional circularly-polarized FM antenna requires that the signals, which will be multiplexed, are within a few mega hertz (MHz) of each other.
Conventional circularly-polarized broadband panel antenna arrays also present problems. For example, broadband panel antenna arrays include three antenna panels, where each panel is designed, such that its width is the same as the width of a face of an antenna tower, which is often between six feet (1.829 meters) and ten feet (3.048 meters). Each panel of the array is placed on a face of an antenna tower. Accordingly, a broadband panel antenna array requires a substantial amount of tower space. In addition, because of the relatively large surface area of a broadband panel, it is capable of being subjected to high windloads.
Further, broadband panel arrays are typically accompanied by complex feed systems that employ semi-flexible coaxial feed lines. The semi-flexible coaxial lines, if inadequately or improperly installed, can become disfigured and cause operational problems.
Accordingly, it would be desirable to provide a reliable circularly-polarized broadband antenna that provides for multi-channel transmission across the full FM band. Additionally, it would be desirable to provide a circularly-polarized broadband antenna that is characterized by low windloads, can provide a compact tower space and/or generates a satisfactorily consistent omnidirectional azimuth pattern.
In one aspect of the present invention, an antenna is provided that includes a mast, a first dipole, and a second dipole, wherein the first dipole crosses with the second dipole, and wherein the first dipole and the second dipole form a first antenna assembly that is coupled to the mast. A hybrid power divider is coupled to the first antenna assembly, and an internal feed system, positioned within the mast, is coupled to the hybrid power divider.
In another aspect of the present invention, an antenna is provided that includes a mast, a first dipole half and a second dipole half that form a first dipole, and a third dipole half and a fourth dipole half that form a second dipole. The first and second dipoles form a first antenna assembly. An internal feed system positioned within the mast, and a means for feeding the first antenna assembly is coupled to the internal feed system and the first antenna assembly.
In yet another aspect of the present invention, a method for transmitting a circularly-polarized signal is provided that includes inputting signal power into a main power divider, transmitting the signal power from the main power divider to main output lines positioned within a mast, transmitting the signal power from the main output lines to a three-way power divider positioned within the mast, transmitting the signal power from the three-way power divider to a two-way power divider positioned external to the mast, transmitting the signal power from the two-way power divider to a hybrid power divider, and transmitting the signal power from the hybrid power divider to crossed dipoles.
There has thus been outlined, rather broadly, the more important features of the invention in order that the detailed description thereof that follows may be better understood, and in order that the present contribution to the art may be better appreciated. There are, of course, additional features of the invention that will be described below and which will form the subject matter of the claims appended hereto.
In this respect, before explaining at least one embodiment of the invention in detail, it is to be understood that the invention is not limited in its application to the details of construction and to the arrangements of the components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced and carried out in various ways. Also, it is to be understood that the phraseology and terminology employed herein, as well as the abstract, are for the purpose of description and should not be regarded as limiting.
As such, those skilled in the art will appreciate that the conception upon which this disclosure is based may readily be utilized as a basis for the designing of other structures, methods and systems for carrying out the several purposes of the present invention. It is important, therefore, that the claims be regarded as including such equivalent constructions insofar as they do not depart from the spirit and scope of the present invention.